National Instruments 320685D-01 User manual

LabWindows/CVI

Programmer

Reference Manual

LabWindows/CVI Programmer Reference Manual

February 1998 Edition

Part Number 320685D-01

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Contents

About This Manual

Organization of This Manual...........................................................................................xiii

Conventions Used in This Manual...................................................................................xiv

Related Documentation.....................................................................................xv

Customer Communication.................................................................................xvi

Chapter 1

LabWindows/CVI Compiler

Overview..........................................................................................................................1-1

LabWindows/CVI Compiler Specifics............................................................................1-1

Compiler Limits.................................................................................................1-1

Compiler Options..............................................................................................1-2

Compiler Defines...............................................................................................1-2

C Language Non-Conformance.......................................................................................1-2

C Language Extensions ...................................................................................................1-2

Keywords That Are Not ANSI C Standard.......................................................1-2

Calling Conventions (Windows 95/NT Only)...................................................1-2

Import and Export Qualifiers.............................................................................1-3

C++ Comment Markers.....................................................................................1-4

Duplicate Typedefs............................................................................................1-4

Structure Packing Pragma (Windows 3.1 and Windows 95/NT Only).............1-4

Program Entry Points (Windows 95/NT Only).................................................1-5

C Library Issues...............................................................................................................1-5

Using the Low-Level I/O Functions..................................................................1-5

C Data Types and 32-Bit Compiler Issues.......................................................................1-6

Data Types.........................................................................................................1-6

Converting 16-Bit Source Code to 32-Bit Source Code ...................................1-6

Debugging Levels............................................................................................................1-8

User Protection ................................................................................................................1-8

Array Indexing and Pointer Protection Errors...................................................1-8

Pointer Arithmetic (Non-Fatal)...........................................................1-8

Pointer Assignment (Non-Fatal).........................................................1-9

Pointer Dereference Errors (Fatal)......................................................1-9

Pointer Comparison (Non-Fatal).........................................................1-10

Pointer Subtraction (Non-Fatal)..........................................................1-10

Pointer Casting (Non-Fatal)................................................................1-10

Dynamic Memory Protection Errors.................................................................1-11

Memory Deallocation (Non-Fatal)......................................................1-11

Memory Corruption (Fatal).................................................................1-11

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General Protection Errors..................................................................................1-11

Library Protection Errors..................................................................................1-11

Disabling User Protection.................................................................................1-12

Disabling Protection Errors at Run-Time...........................................1-12

Disabling Library Errors at Run-Time ...............................................1-12

Disabling Protection for Individual Pointer........................................1-12

Disabling Library Protection Errors for Functions............................. 1-13

Details of User Protection.................................................................................1-14

Pointer Casting ...................................................................................1-14

Dynamic Memory...............................................................................1-15

Avoid Unassigned Dynamic Allocation in

Function Parameters.......................................................... 1-15

Library Functions ...............................................................................1-16

Unions................................................................................................. 1-16

Stack Size ........................................................................................................................ 1-16

Include Paths ...................................................................................................................1-17

Include Path Search Precedence .......................................................................1-17

Chapter 2

Using Loadable Compiled Modules

About Loadable Compiled Modules ...............................................................................2-1

Advantages and Disadvantages of Using Loadable Compiled Modules

in LabWindows/CVI......................................................................................2-2

Using a Loadable Compiled Module as an Instrument Driver

Program File...................................................................................................2-2

Using a Loadable Compiled Module as a User Library....................................2-3

Using a Loadable Compiled Module in the Project List................................... 2-3

Using a Loadable Compiled Module as an External Module........................... 2-4

Notification of Changes in Run State ...............................................................2-4

Example 1...........................................................................................2-5

Example 2...........................................................................................2-6

Using Run State Change Callbacks in a DLL...................................................2-6

Compiled Modules that Contain Asynchronous Callbacks ..............................2-7

Chapter 3

Windows 95/NT Compiler/Linker Issues

Loading 32-Bit DLLs under Windows 95/NT ................................................................3-1

DLLs for Instrument Drivers and User Libraries..............................................3-2

Using The LoadExternalModule Function .......................................................3-2

Link Errors when Using DLL Import Libraries................................................3-2

DLL Path (.pth) Files Not Supported................................................................3-2

16-Bit DLLs Not Supported..............................................................................3-2

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Run State Change Callbacks in DLLs...............................................................3-2

DllMain..............................................................................................................3-3

Releasing Resources when a DLL Unloads ......................................................3-3

Generating an Import Library............................................................................3-4

Default Unloading/Reloading Policy ................................................................3-4

Compatibility with External Compilers...........................................................................3-4

Choosing Your Compatible Compiler...............................................................3-5

Object Files, Library Files, and DLL Import Libraries.....................................3-5

Compatibility Issues in DLLs............................................................................3-5

Structure Packing................................................................................3-6

Bit Fields.............................................................................................3-6

Returning Floats and Doubles.............................................................3-7

Returning Structures ...........................................................................3-7

Enum Sizes..........................................................................................3-7

Long Doubles......................................................................................3-7

Differences between LabWindows/CVI and the External Compilers...............3-7

External Compiler Versions Supported.............................................................3-8

Required Preprocessor Definitions....................................................................3-8

Multithreading and the LabWindows/CVI Libraries.......................................................3-8

Using LabWindows/CVI Libraries in External Compilers..............................................3-9

Include Files for the ANSI C Library and the LabWindows/CVI

Libraries..........................................................................................................3-10

Standard Input/Output Window ........................................................................3-10

Resolving Callback References from .UIR Files ..............................................3-10

Linking to Callback Functions Not Exported from a DLL.................3-11

Resolving References from Modules Loaded at Run-Time..............................3-12

Resolving References to the LabWindows/CVI

Run-Time Engine.............................................................................3-12

Resolving References to Symbols Not in Run-Time Engine..............3-12

Resolving Run-Time Module References to Symbols

Not Exported from a DLL................................................................3-13

Run State Change Callbacks Are Not Available in External Compilers...........3-13

Calling InitCVIRTE and CloseCVIRTE...........................................................3-14

Watcom Stack Based Calling Convention ........................................................3-15

Using Object and Library Files in External Compilers ...................................................3-15

Default Library Directives.................................................................................3-15

Microsoft Visual C/C++ .....................................................................3-16

Borland C/C++....................................................................................3-16

Watcom C/C++...................................................................................3-16

Symantec C/C++.................................................................................3-16

Borland Static versus Dynamic C Libraries......................................................3-17

Borland Incremental Linker ..............................................................................3-17

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Borland C++ Builder......................................................................................... 3-17

Watcom Pull-in References ..............................................................................3-17

Creating Object and Library Files in External Compilers for Use

in LabWindows/CVI.....................................................................................................3-18

Microsoft Visual C/C++ ...................................................................................3-18

Borland C/C++..................................................................................................3-18

Watcom C/C++.................................................................................................3-19

Symantec C/C++...............................................................................................3-19

Creating Executables in LabWindows/CVI ....................................................................3-20

Creating DLLs in LabWindows/CVI ..............................................................................3-20

Customizing an Import Library.........................................................................3-20

Preparing Source Code for Use in a DLL......................................................... 3-21

Calling Convention for Exported Functions....................................... 3-21

Exporting DLL Functions and Variables............................................3-22

Include File Method............................................................................3-22

Export Qualifier Method ....................................................................3-22

Marking Imported Symbols in Include File Distributed

with DLL ......................................................................................... 3-23

Recommendations .............................................................................. 3-24

Automatic Inclusion of Type Library Resource for Visual Basic ....................3-24

Creating Static Libraries in LabWindows/CVI...............................................................3-25

Creating Object Files in LabWindows/CVI ....................................................................3-26

Calling Windows SDK Functions in LabWindows/CVI.................................................3-26

Windows SDK Include Files............................................................................. 3-26

Using Windows SDK Functions for User Interface Capabilities .....................3-27

Using Windows SDK Functions to Create Multiple Threads...........................3-27

Automatic Loading of SDK Import Libraries................................................... 3-27

Setting Up Include Paths for LabWindows/CVI, ANSI C, and SDK Libraries..............3-28

Compiling in LabWindows/CVI for Linking in LabWindows/CVI.................3-28

Compiling in LabWindows/CVI for Linking in an External Compiler............3-28

Compiling in an External Compiler for Linking in an External Compiler.......3-28

Compiling in an External Compiler for Linking in LabWindows/CVI............3-29

Handling Hardware Interrupts under Windows 95/NT................................................... 3-29

Chapter 4

Windows 3.1 Compiler/Linker Issues

Using Modules Compiled by LabWindows/CVI............................................................4-1

Using 32-Bit Watcom Compiled Modules under Windows 3.1...................................... 4-1

Using 32-Bit Borland or Symantec Compiled Modules under Windows 3.1.................4-2

16-Bit Windows DLLs....................................................................................................4-3

Helpful LabWindows/CVI Options for Working with DLLs...........................4-4

DLL Rules and Restrictions..............................................................................4-4

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DLL Glue Code.................................................................................................4-7

DLLs That Can Use Glue Code Generated at Load Time..................4-8

DLLs That Cannot Use Glue Code Generated at Load Time.............4-8

Loading a DLL That Cannot Use Glue Code Generated

at Load Time....................................................................................4-8

Rules for the DLL Include File Used to

Generate Glue Source........................................................4-9

If the DLL Requires a Support Module outside the DLL.....4-9

If You Pass Arrays Bigger Than 64 K to the DLL...............4-9

If the DLL Retains a Buffer after the Function Returns

(an Asynchronous Operation)............................................4-11

If the DLL Calls Directly Back into 32-Bit Code ................4-12

If the DLL Returns Pointers .................................................4-15

If a DLL Receives a Pointer that Points to Other

Pointers ..............................................................................4-18

DLL Exports Functions by Ordinal Value Only ..................4-20

Recognizing Windows Messages Passed from a DLL......................................4-21

Creating 16-bit DLLs with Microsoft Visual C++ 1.5......................................4-21

Creating 16-bit DLLs with Borland C++ ..........................................................4-22

DLL Search Precedence....................................................................................4-23

Chapter 5

UNIX Compiler/Linker Issues

Calling Sun C Library Functions.....................................................................................5-1

Restrictions on Calling Sun C Library Functions..............................................5-1

Using Shared Libraries in LabWindows/CVI..................................................................5-2

Using dlopen......................................................................................................5-2

The LabWindows/CVI Run-Time Engine as a Shared Library.......................................5-2

Creating Executables that Use the LabWindows/CVI Libraries .....................................5-3

Compatible External Compilers........................................................................5-3

Static and Shared Versions of the ANSI C and Other Sun Libraries................5-3

Non-ANSI Behavior of Sun Solaris 1 ANSI C Library....................................5-4

LabWindows/CVI Implements printf and scanf................................................5-4

Main Function Must Call InitCVIRTE..............................................................5-4

Run State Change Callbacks Are Not Available in Executables ......................5-5

Using Externally Compiled Modules ..............................................................................5-6

Restrictions on Externally Compiled Modules..................................................5-6

Compiling Modules With External Compilers..................................................5-6

Locking Process Segments into Memory Using plock() .................................................5-7

UNIX Asynchronous Signal Handling............................................................................5-7

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Solaris 1 ANSI C Library Implementation...................................................................... 5-8

Replacement Functions.....................................................................................5-9

Additional Functions Not Found in Sun Solaris 1 libc.....................................5-9

Incompatibilities among LabWindows/CVI, Sun Solaris, and ANSI C .........................5-10

Between LabWindows/CVI and ANSI C ......................................................... 5-10

Between LabWindows/CVI and Sun Solaris....................................................5-11

Chapter 6

Building Multiplatform Applications

Multiplatform Programming Guidelines.........................................................................6-1

Library Issues....................................................................................................6-1

Externally Compiled Modules ..........................................................................6-3

Multiplatform User Interface Guidelines ........................................................................6-3

Chapter 7

Creating and Distributing Standalone Executables and DLLs

Introduction to the Run-Time Engine..............................................................................7-1

Distributing Standalone Executables under Windows...................................... 7-1

Minimum System Requirements for Windows 95/NT.......................7-1

No Math Coprocessor Required for Windows 95/NT........................ 7-2

Minimum System Requirements for Windows 3.1............................ 7-2

Math Coprocessor Software Emulation for Windows 3.1..................7-2

Distributing Standalone Executables under UNIX........................................... 7-2

Distributing Standalone Executables under Solaris 2.........................7-3

Distributing Standalone Executables under Solaris 1.........................7-4

Minimum System Requirements for UNIX........................................7-5

Translating the Message File ............................................................................7-5

Configuring the Run-Time Engine..................................................................................7-5

Solaris 1 Patches Required for Running Standalone Executable......................7-5

Configuration Option Descriptions...................................................................7-6

cvirtx (Windows 3.1 Only).................................................................7-6

cvidir (Windows Only).......................................................................7-7

useDefaultTimer (Windows Only).....................................................7-7

DSTRules............................................................................................7-7

UNIX Options.....................................................................................7-7

Necessary Files for Running Executable Programs........................................................7-8

Necessary Files for Using DLLs Created in Windows 95/NT........................................ 7-9

Location of Files on the Target Machine for Running Executables and DLLs...............7-9

LabWindows/CVI Run-Time Engine under Windows 95/NT .........................7-10

Run-Time Library DLLs ....................................................................7-10

Low-Level Support Driver .................................................................7-10

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Message, Resource, and Font Files.....................................................7-11

National Instruments Hardware I/O Libraries ....................................7-11

LabWindows/CVI Run-Time Engine under Windows 3.1 ...............................7-11

LabWindows/CVI Run-Time Engine under Sun Solaris ..................................7-12

Rules for Accessing UIR, Image, and Panel State Files on All Platforms........7-12

Rules for Using DLL Files under Windows 95/NT ..........................................7-13

Rules for Using DLL Files under Windows 3.1................................................7-13

Rules for Loading Files Using LoadExternalModule .......................................7-14

Forcing Modules that External Modules Refer to

into Your Executable or DLL ..........................................................7-15

Using LoadExternalModule on Files in the Project............................7-15

Using LoadExternalModule on Library and Object Files

Not in the Project .............................................................................7-16

Using LoadExternalModule on DLL Files under

Windows 95/NT...............................................................................7-17

Using LoadExternalModule on DLL and Path Files

under Windows 3.1 ..........................................................................7-17

Using LoadExternalModule on Source Files (.c)................................7-18

Rules for Accessing Other Files........................................................................7-19

Error Checking in Your Standalone Executable or DLL ..................................7-19

Chapter 8

Distributing Libraries and Function Panels

How to Distribute Libraries.............................................................................................8-1

Adding Libraries to User’s Library Menu.......................................................................8-1

Specifying Library Dependencies....................................................................................8-2

Chapter 9

Checking for Errors in LabWindows/CVI

Error Checking.................................................................................................................9-2

Status Reporting by LabWindows/CVI Libraries and Instrument Drivers......................9-3

User Interface Library .......................................................................................9-3

Analysis/Advanced Analysis Libraries .............................................................9-3

Easy I/O for DAQ Library.................................................................................9-4

Data Acquisition Library...................................................................................9-4

VXI Library.......................................................................................................9-4

GPIB/GPIB 488.2 Library.................................................................................9-4

RS-232 Library..................................................................................................9-5

VISA Library.....................................................................................................9-5

IVI Library.........................................................................................................9-5

TCP Library.......................................................................................................9-6

DDE Library......................................................................................................9-6

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ActiveX Automation Library............................................................................9-6

X Property Library............................................................................................9-6

Formatting and I/O Library...............................................................................9-6

Utility Library................................................................................................... 9-7

ANSI C Library.................................................................................................9-7

LabWindows/CVI Instrument Drivers..............................................................9-7

Appendix A

Errors and Warnings

Appendix B

Customer Communication

Glossary

Figures

Figure 7-1. Files Necessary to Run a LabWindows/CVI Executable Program

on a Target Machine...........................................................................7-8

Tables

Table 1-1. LabWindows/CVI Compiler Limits .......................................................1-1

Table 1-2. LabWindows/CVI Allowable Data Types.............................................. 1-6

Table 1-3. Stack Size Ranges for LabWindows/CVI............................................... 1-16

Table 7-1. LabWindows/CVI Run-Time Engine Files ............................................7-10

Table 7-2. Windows NT Registry Entry Values for the Low-Level

Support Driver....................................................................................7-11

Table 7-3. Pathnames and Targets of Links.............................................................7-12

Table A-1. Error Messages........................................................................................A-1

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National Instruments Corporation xiii LabWindows/CVI Programmer Reference Manual

About This Manual

The LabWindows/CVI Programmer Reference Manual contains

information to help you develop programs in LabWindows/CVI. The

LabWindows/CVI Programmer Reference Manual is intended for use by

LabWindows users who have already completed the Getting Started with

LabWindows/CVI tutorial. To use this manual effectively, you should be

familiar with Getting Started with LabWindows/CVI, the LabWindows/CVI

User Manual, DOS, Windows, and the C programming language.

Organization of This Manual

The LabWindows/CVI Programmer Reference Manual is organized as

follows:

• Chapter 1, LabWindows/CVI Compiler, describes LabWindows/CVI

compiler specifics, C language extensions, 32-bit compiler issues,

debugging levels, and user protection.

• Chapter 2, Using Loadable Compiled Modules, describes the

advantages and disadvantages of using compiled code modules in your

application. It also describes the kinds of compiled modules available

in LabWindows/CVI and includes programming guidelines for

modules you generate with external compilers.

• Chapter 3, Windows 95/NT Compiler/Linker Issues, describes the

different kinds of compiled modules available under

LabWindows/CVI for Windows 95/NT and includes programming

guidelines for modules you generate with external compilers.

• Chapter 4, Windows 3.1 Compiler/Linker Issues, describes the

different kinds of compiled modules available under

LabWindows/CVI for Windows 3.1 and includes programming

guidelines for modules you generate with external compilers.

• Chapter 5, UNIX Compiler/Linker Issues, describes the kinds of

compiled modules available under LabWindows/CVI for UNIX and

includes programming guidelines for modules you generate with

external compilers.

• Chapter 6, Building Multiplatform Applications, contains guidelines

and caveats for writing platform-independent LabWindows/CVI

applications. LabWindows/CVI currently runs under Windows 3.1

and Windows 95/NT for the PC, and Solaris 1 and Solaris 2 for the

SPARCstation.

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LabWindows/CVI Programmer Reference Manual xiv

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• Chapter7, Creating and Distributing Standalone Executables and

DLLs, describes how the LabWindows/CVI Run-time Engine, DLLs,

externally compiled modules, and other files interact with your

executable file. This chapter also describes how to perform error

checking in a standalone executable program. You can create

executable programs from any project that runs in the

LabWindows/CVI environment.

• Chapter8, Distributing Libraries andFunction Panels, describes how

to distribute libraries, add libraries to a user’s Library menu, and

specify library dependencies.

• Chapter9, Checking for Errors in LabWindows/CVI, describes

LabWindows/CVI error checking and how LabWindows/CVI reports

errors in LabWindows/CVI libraries and compiled external modules.

•AppendixA, Errors and Warnings, contains an alphabetized list of

compiler warnings, compiler errors, link errors, DLL loading errors,

and external module loading errors generated by LabWindows/CVI.

•AppendixB, Customer Communication, contains forms to help you

gather the information necessary to help us solve your technical

problems and a form you can use to comment on the product

documentation.

•The Glossary contains an alphabetical list of terms used in this manual

and a description of each.

•The Index contains an alphabetical list of key terms and topics used in

this manual, including the page where each one can be found.

Conventions Used in This Manual

The following conventions are used in this manual.

<> Angle brackets enclose the name of a key on the keyboard—for example,

<Shift>.

- A hyphen between two or more key names enclosed in angle brackets

denotes that you should simultaneously press the named keys—for

example, <Ctrl-Alt-Delete>.

» The » symbol leads you through nested menu items and dialog box options

to a final action. The sequence File»Page Setup»Options» Substitute

Fonts directs you to pull down the File menu, select the PageSetup item,

select Options, and finally select the Substitute Fonts options from the

last dialog box.

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National Instruments Corporation xv LabWindows/CVI Programmer Reference Manual

This icon to the left of bold italicized text denotes a note, which alerts you

to important information.

This icon to the left of bold italicized text denotes a caution, which advises

you of precautions to take to avoid injury, data loss, or a system crash.

bold Bold text denotes the names of menus, menu items, parameters, or dialog

box buttons.

bold italic Bold italic text denotes an activity objective, note, caution, or warning.

italic Italic text denotes variables, emphasis, a cross reference, or an introduction

to a key concept. This font also denotes text from which you supply the

appropriate word or value.

monospace Text in this font denotes text or characters that you should literally enter

from the keyboard, sections of code, programming examples, and syntax

examples. This font is also used for the proper names of disk drives, paths,

directories, programs, functions, filenames and extensions, and for

statements and comments taken from programs.

monospace bold Bold text in this font denotes the messages and responses that the computer

automatically prints to the screen.

monospace italic

Italic text in this font denotes that you must enter the appropriate words or

values in the place of these items.

paths Paths in this manual are denoted using backslashes (\) to separate drive

names, directories, folders, and files.

Related Documentation

You may find the following documentation helpful while programming in

LabWindows/CVI:

• Microsoft Developer Network CD, Microsoft Corporation,

Redmond WA

• Programmer’s Guide to Microsoft Windows 95, Microsoft Press,

Redmond WA, 1995

• Harbison, Samuel P. and Guy L. Steele, Jr., C: A Reference Manual,

Englewood Cliffs, NJ: Prentice-Hall, Inc., 1995

!

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About This Manual

LabWindows/CVI Programmer Reference Manual xvi

©

National Instruments Corporation

Customer Communication

National Instruments wants to receive your comments on our products and

manuals. We are interested in the applications you develop with our

products, and we want to help you if you have problems with them. To

make it easy for you to contact us, this manual contains comment and

technical support forms for you to complete. These forms are in

Appendix B, Customer Communication, at the end of this manual.

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1

LabWindows/CVI Compiler

This chapter describes LabWindows/CVI compiler specifics, C language extensions, 32-bit

compiler issues, debugging levels, and user protection.

Overview

The LabWindows/CVI compiler is a 32-bit ANSI C compiler. The kernel of the

David R. Hanson). It is not an optimizing compiler, but instead focuses on debugging, user

protection, and platform independence. Because the compiler is an integral part of the

LabWindows/CVI environment and features a limited set of straightforward options, it is also

easy to use.

LabWindows/CVI Compiler Specifics

This section describes specific LabWindows/CVI compiler limits, options, defines, and

diversions from the ANSI C standard.

Compiler Limits

Table 1-1 shows the compiler limits for LabWindows/CVI.

Table 1-1.

LabWindows/CVI Compiler Limits

Coding Attribute Limit

Maximum nesting of #include 32

Maximum nesting of #if, #ifdef 16

Maximum number of macro parameters 32

Maximum number of function parameters 64

Maximum nesting of compound blocks 32

Maximum size of array/struct types 2

31

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Compiler Options

You can set the LabWindows/CVI compiler options by selecting Options»Compiler Options

in the Project window. This command opens a dialog box that allows you to set

LabWindows/CVI compiler options. For a discussion of these options, refer to the Compiler

Options section in Chapter 3, Project Window, of the LabWindows/CVI User Manual.

Compiler Defines

The LabWindows/CVI compiler accepts compiler defines through the Compiler Defines

command in the Options menu of the Project window. For more information, refer to the

Compiler Defines section in Chapter 3, Project Window, of the LabWindows/CVI User

Manual.

C Language Non-Conformance

LabWindows/CVI for UNIX does not allow you to pass a struct as one of a series of

unspecified variable arguments. Because of this,

va_arg (ap, type) is not legal in

LabWindows/CVI if

type is a struct type.

LabWindows/CVI accepts the

#line preprocessor directive, but ignores it.

C Language Extensions

The LabWindows/CVI compiler has several extensions to the C language. The purpose is to

make the LabWindows/CVI compiler compatible with the commonly used C extensions in

external compilers under Windows 95/NT.

Keywords That Are Not ANSI C Standard

LabWindows/CVI for Windows 3.1 accepts the non-ANSI C keywords pascal, PASCAL, and

_pascal, but ignores them.

Calling Conventions (Windows 95/NT Only)

You can use the following calling convention qualifiers in function declarations:

cdecl

_cdecl

__cdecl

(recommended)

_stdcall

__stdcall

(recommended)

In Microsoft Visual C/C++, Borland C/C++, and Symantec C/C++, the calling convention

normally defaults to __

cdecl if you do not use a calling convention qualifier. You can,

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however, set options to cause the calling convention to default to __stdcall. The behavior

is the same in LabWindows/CVI. You can set the default calling convention to either __

cdecl

or

__stdcall using the Compiler Options command in the Options menu of the Project

window. When you create a new project, the default calling convention is

__cdecl.

In Watcom C/C++, the default calling convention is not __

cdecl or __stdcall. You must

use the

-4s (80486 Stack-Based Calling) option when you compile a module in Watcom for

use in LabWindows/CVI. Refer to the Compatibility with External Compilers section in

Chapter 3, Windows 95/NT Compiler/Linker Issues. The

-4s option causes the stack-based

calling convention to be the default. In LabWindows/CVI under Watcom compatibility mode,

the default calling convention is always the stack-based convention. It cannot be changed. The

LabWindows/CVI compiler accepts the

__cdecl and __stdcall conventions under

Watcom, except that floating point and structure return values do not work in the

__cdecl

calling convention. National Instruments recommends that you avoid using

__cdecl with

Watcom.

In the

__cdecl calling convention and the Watcom stack-based calling convention, the

calling function is responsible for cleaning up the stack. Functions can have a variable number

of arguments.

In the

__stdcall calling convention, the called function is responsible for cleaning up the

stack. Functions with a variable number of arguments do not work in

__stdcall. If you use

the

__stdcall qualifier on a function with a variable number of arguments,

LabWindows/CVI does not honor the qualifier. All compilers pass parameters and return

values in the same way for

__stdcall functions, except for floating point and structure

return values.

National Instruments recommends the

__stdcall calling convention for all functions

exported from a DLL, except functions with a variable number of arguments. Visual Basic

and other non-C Windows programs expect DLL functions to be

__stdcall.

Import and Export Qualifiers

You can use the following qualifiers in variable and function declarations:

__declspec(dllimport)

__declspec(dllexport)

__import

__export

_import

_export

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At this time, not all these qualifiers work in all external compilers. The LabWindows/CVI

cvidef.h include file defines the following macros, which are designed to work in each

external compiler.

DLLIMPORT

DLLEXPORT

An import qualifier informs the compiler that the symbol is defined in a DLL. Declarations

of variables imported from a DLL require import qualifiers, but function declarations do not.

An export qualifier is relevant only in a project for which the target type is Dynamic Link

Library. The qualifier can be on the declaration or definition of the symbol, or both. The

qualifier instructs the linker to include the symbol in the DLL import library.

C++ Comment Markers

You can use double slashes (//) to begin a comment. The comment continues until the end of

the line.

Duplicate Typedefs

The LabWindows/CVI compiler does not report an error on multiple definitions of the same

typedef identifier, as long as the definitions are identical.

Structure Packing Pragma (Windows 3.1 and Windows 95/NT Only)

The pack pragma can be used within LabWindows/CVI to specify the maximum alignment

factor for elements within a structure. For example, assume the following structure definition:

struct t {

double d1;

char charVal;

short shortVal;

double d2;

};

If the maximum alignment is 1, the compiler can start the structure on any 1-byte boundary

and inserts no gaps between the structure elements.

If the maximum alignment is 8, the compiler must start the structure on an 8-byte boundary,

place

shortVal on a 2-byte boundary, and place d2 on an 8-byte boundary.

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You can set the maximum alignment as follows:

#pragma pack(4) /* sets maximum alignment to 4 bytes */

#pragma pack(8) /* sets maximum alignment to 8 bytes */

#pragma pack() /* resets to the default*/

The maximum alignment the compiler applies to a structure is based on the last pack

pragma

statement it sees before the definition of the structure.

Program Entry Points (Windows 95/NT Only)

Under Windows 95/NT, you can use WinMain instead of main as the entry-point function to

your program. You might want to do this if you plan to link your executable using an external

compiler. You must include

windows.h for the data types that normally appear in the

WinMain parameter list. The following is the prototype for WinMain with the Windows data

types reduced to intrinsic C types.

int __stdcall WinMain(void * hInstance, void * hPrevInstance,

char * lpszCmdLine int nCmdShow)

C Library Issues

This section discusses special considerations in LabWindows/CVI in the areas of low-level

I/O functions and the UNIX C library.

Using the Low-Level I/O Functions

Many functions in the UNIX libraries and the C compiler libraries for the PC are not ANSI C

Standard Library functions. In general, LabWindows/CVI implements the ANSI C Standard

Library. Under UNIX, you can call UNIX libraries for the non-ANSI C functions in

conjunction with LabWindows/CVI.

The low-level I/O functions

open, close, read, write, lseek, and eof are not in the

ANSI C Standard Library. Under UNIX, these functions are available in the UNIX C library.

Refer to Chapter 5, UNIX Compiler/Linker Issues, for more information.

Under Windows, you can use these functions along with

sopen and fdopen if you include

lowlvlio.h.

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